In the state of the art, this type of instrument comprises at least two boxes movable relative to each other by being moved towards each other or away from each other by the player. Generally, the boxes are interconnected by a bellows defining an air supply that is of variable capacity and that is in communication with a series of cells formed in boards carried by the boxes. Each cell is provided with two free reeds that are caused to vibrate by the inward or outward flow of air corresponding to the bellows being filled or emptied.
The cells are fitted with valves which, on being opened and closed, determine whether or not the reeds are engaged by the flow of air. The valves are controlled by a mechanism including in particular keys mounted on the boxes to be actuated by the player.
In conventional manner, the box for the right hand remains stationary, being supported by straps, while the box for the left hand moves to expand or to squeeze the bellows. It should also be observed that the musician must carry the weight of the box in the left hand, while simultaneously seeking to perform the part of the music that is for the left hand.